This invention relates to novel mixtures of amines as catalysts for the formation of urethane cellular products, particularly polyester urethane foams.
It is well known that the urethane linkages of urethane foams are formed by the exothermic reaction of a polyfunctional isocyanate and a polyfunctional active hydrogen-containing compound in the presence of a catalyst, and that the cellular structure of the foam is provided by gas evolution and expansion during the urethane-forming reaction. From the standpoint of their chemical structure, urethanes are usually classified as polyether or polyester urethanes, depending on the type of polyol employed. Urethane foams also differ with respect to their physical structure and, from this standpoint, are generally classified as flexible, semi-flexible or rigid foams.
It is also known that a number of different chemical reactions occur during polymer formation and expansion. For example, in addition to the chain-extending, urethane-forming reaction between free isocyanate groups and active hydrogen, initially formed urethane linkages bearing secondary hydrogen may alo function as a source of active hydrogen and react with additional isocyanate to form cross-links between polymer chains. Further, in water-containing systems such as those employed for the manufacture of flexible foams, isocyanate is also consumed by reaction with water, thereby generating carbon dioxide as an in situ blowing agent and introducing urea groups. These reactions, their relative rates and the point in time at which they occur influence the nature of the cellular structure and the physical and mechanical properties of the foam produced. Although balancing these variables so as to achieve a particular type or grade of foam can be controlled to some extent by the functionality, molecular weight and other structural features of the reactants, the catalyst system also plays a significant role in this respect. Among the relatively few compounds that have achieved widespread commercial application as catalysts in polyurethane manufacture are the tertiary amines consisting of carbon, hydrogen and nitrogen and those consisting of carbon, hydrogen, nitrogen and oxygen. N,N-Dimethyl ethanolamine is commonly employed by those skilled in the art as a catalyst for the preparation of polyurethane foam. 2-(2-Dimethyl-aminoethoxy)ethanol has been mentioned as a catalyst for polyurethane coatings in British Pat. No. 1,166,742. 3-Dimethylaminopropionitrile was reported as a catalyst for polyurethane foams in U.S. Pat. No. 3,925,268. N-Ethylmorpholine is a major component in the mixed catalyst systems for high-resilience foams. N,N,N,N-Tetramethyl-1,3-butane-diamine is another known catalyst for urethane foams.
With respect to flexible polyurethane foam manufacture generally, it is often the preferred practice of foam manufactures to premix the catalyst, water and foam stabilizes and to feed the aqueous premixture, commonly referred to as the activator stream, to the foam formulation as a single stream. It is often observed that the mere mixing of the catalyst and the foam stabilizing components in water forms a highly viscous mixture which detracts from the processing advantage of adding these components as a combined stream rather than as individual streams. This problem is encountered in particular in the manufacture of polyester polyol-based polyurethanes in which silicon-free organic surfactants are employed. Thus, when certain catalysts, such as bis-[2-(N,N-dimethylamino)ethyl]ether, are present in combination with organic foam stabilizers, the activator stream becomes extremely viscous, approaching or actually undergoing gellation. This problem is often resolved by the use of N-ethylmorpholine as the catalyst.
The usefulness of N-ethylmorpholine in the manufacture of cellular urethanes is, however, attended with certain disadvantages. Thus, N-ethylmorpholine suffers most from having a particularly strong amine odor. The large quantities of N-ethylmorpholine which are employed relative to other catalyst components of the foam formulation causes an obnoxious atmosphere at and surrounding the foam manufacturing plant site. Also, foams prepared with N-ethylmorpholine have a strong residual amino odor. Finally, N-ethylmorpholine has been associated with a number of toxic effects as reported in Plastic Technology, "Catalysts Improve As Their Need Increases", pages 47-49 (July 1972). Consequently, it is desirable and a primary object of this invention to provide a novel catalyst replacement for N-ethylmorpholine in the production of cellular polyurethane foams. Furthermore, the novel catalyst should have sufficient pre-mix activator stability and mix viscosity to compare favorably with existing commercial systems. Various other objects and advantages of the present invention will become apparent from the accompanying description and disclosure.